1. Field of the Invention
The present invention relates generally to a rotation adjusting apparatus and, more particularly, is directed to apparatus for adjusting the height or angle of the seats of an automobile.
2. Description of the Prior Art
In the prior art seats for automobiles and the like, the sitting height and/or sitting angle can be changed in accordance with driver's physique and taste.
In such seats hinge arms provided in the front and rear of the seat frame are pivoted to leg members which are fixed to a seat adjuster provided along the floor. The seat frame is moved up and down by the turning force acting on the hinge arms. An operating apparatus is coupled to the hinge arms and the height of the seat is adjusted by operating this operating apparatus. This operating apparatus employs a friction brake as a lock mechanism which disables the lifting operation at the desired height of the seat.
By way of example, such prior art brake apparatus is disclosed in the published document of unexamined Japanese patent application No. 29827/1984. This brake apparatus includes a brake drum which is fixed to a seat frame within which there are respectively provided a lever plate which is fixed to a drive shaft supported at a center opening of a drum bottom wall and a hanger engaged with the drive shaft so as to be rotatable and which is fixed to a shaft to be driven through a serration. A handle is fixed to the drive shaft and a coupling member for the seat lifting mechanism is attached to the shaft to be driven. A pair of guides are provided between the lever plate and the hanger and both guides are coupled to both ends of a brake spring that is urged against the inner peripheral surface of the brake drum. There is provided a contact portion. This contact portion contacts the hanger to thereby inhibit the hanger from moving when the lever plate is stopped. Further, there is provided a cam portion which is engaged with the lever plate when the lever plate is rotated. According to this friction brake apparatus, upon the initial rotation of the lever plate, the contact protion is swayed by the engagement between the cam portion and the lever plate to thereby release it from contact with the hanger and thus forming a spacing or clearance between the contact portion and the hanger. By this clearance, the diameter of the brake spring is reduced so as to decrease its force contacting the inner peripheral surface of the brake drum, whereby the friction brake is released, and the shaft to be driven is made rotatable.
In this prior art friction brake apparatus, the shaft to be driven is friction-locked by contacting the brake spring with the inner peripheral surface of the brake drum so that when a large load acts in the downward direction such as an impact force applied to the seat, applying a rotating force on the shaft to be driven the brake spring is slidably moved within the brake drum and thus there is a fear that the seat will be moved downward beyond the predetermined height. Further, since the brake operation is carried out by increasing or decreasing the winding diameter of the brake spring, it is very difficult to precisely lock the seat at a desired height. In addition, upon operation, a so-called dragging phenomenon in which the brake spring is slidably moved in contact with the inner peripheral surface of the brake drum will occur. There is then a defect that the operation is not carried out smoothly.